Metal Nanoparticles: Silver
The metal nanoparticles can be classified into three main categories: clusters, nanodomains, and colloids. The contemporary approach to produce silver and gold nanoparticles using “green” reducing agents. For example, silver nanoparticles were produced using tannic acid as a reducing agent, but also the tannins of green and black tea are able to cause the formation of silver nanoparticles. The most interesting thing of these green synthesis of silver or gold nanoparticles is the fact that the green, reducing agent is coming from renewable sources, and it is able not only to cause the reduction of the metal but also to act as capping agent, undergoing an adsorption on the metal particles surface and favoring the stabilization of the colloidal suspension. A less common method for the preparation of silver nanoparticles dispersion regards the use of high-intensity ultrasonic waves to fragment and disperse the metal particles. Metal nanoparticles, in particular silver, copper and gold nanoparticles have an antibacterial activity.